Passive dosing dispensers of various geometries are disclosed in prior art patents. For instance, U.S. Pat. No. 650,161 which issued to J. Williams et al. on May 22, 1900 and U.S. Pat. No. 1,175,032 which issued to E. R. Williams on Mar. 14, 1916 disclose passive dispensers which are alternately flooded and then syphoned to a predetermined level. Also, U.S. Pat. No. 3,772,715 which issued to Nigro on Nov. 20, 1973, and U.S. Pat. No. 3,781,926 which issued to Levey on Jan. 1, 1974, and U.S. Pat. No. 3,943,582 which issued to Daeninckx et al. on Mar. 16, 1976 disclose passive dispensers which are alternately flooded and then gravitationally drained. Moreover, U.S. Pat. No. 3,407,412 which issued to Spear on Oct. 29, 1968, and U.S. Pat. No. 3,444,566 which issued to Spear on May 20, 1969 disclose dispensers which, although they have no moving parts, must be connected to a pressurized water supply such as the trap refill tube in a toilet tank and in which the direction of flow alternates in labyrinth passages.
U.S. Pat. No. 1,144,525 issued to Blake on June 29, 1915 discloses a passive liquid dispensing apparatus employing an inverted J-shaped syphon tube to dispense a dilute liquid product solution as the water level in the tank is lowered. However, the dilute liquid product solution contained within the dispensing chamber is not isolated from the remainder of the toilet tank water during quiescent periods intermediate flush cycles. U.S. Pat. No. 2,839,763 issued to Newsom on June 24, 1958 discloses a bottle containing a liquid disinfectant and equipped with a screw cap which also functions as the product dispensing apparatus. As the toilet tank water rises, it traps a pocket of air in chamber 36 which is connected by virtue of passageway 40 to the liquid disinfectant which is substantially even with the lowermost end of the container neck. As the water level in the tank continues to rise, air is pumped into the container to vitiate the partial vacuum existing therewithin. In addition, the pumping action causes a portion of the liquid disinfectant contained in the cap to be pumped through passageway 44 and out discharge port 30 in response to the rising water level. However, the liquid disinfectant is injected into the toilet tank as the water level rises, i.e., at a point in the flush cycle when it is least likely to be effective in cleansing and/or disinfecting the toilet bowl. U.S. Pat. No. 2,812,119 issued to Bethune on Nov. 5, 1957 discloses a liquid dispenser which incorporates a pumping cycle to fill a reservoir as the water level rises. However, the reservoir is thereafter allowed to drain by gravity at a controlled rate into the liquid contained in the toilet tank. Accordingly, the dispensed material is added during quiescent periods intermediate flush cycles when it is least likely to be effective in cleansing and/or disinfecting the toilet bowl.
U.S. Pat. No. 2,688,754 issued to Willits et al. on Sept. 14, 1954, U.S. Pat. No. 3,073,488 issued to Komter on Jan. 15, 1963, U.S. Pat. No. 3,864,763 issued to Spransy on Jan. 11, 1975 and U.S. Pat. No. 3,965,497 issued to Corsette on June 29, 1976 disclose various forms of prior art liquid dispensers which are passive and which dispense liquid material in response to lowering of the water level in the toilet tank.
However, none of the above noted prior art references disclose means for discharging a predetermined dose-volume of liquid product solution in response to a decreasing water level in combination with the other desirable dispenser characteristics provided by the present invention, i.e., passivity, constant volume discharge regardless of depth of immersion, and product solution isolation from the toilet tank water during quiescent periods intermediate flush cycles.